Guarantor and Nonguarantor Financial Statements - Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Statement of Income Captions [Line Items]
Revenue	$ 23,894,091	$ 21,340,088	$ 18,628,787
Cost of revenue	18,689,013	16,449,212	14,305,099
Operating, administrative and other	3,436,009	3,365,773	2,858,720
Depreciation and amortization	439,224	451,988	406,114
Intangible asset impairment	89,787
Total costs and expenses	22,654,033	20,266,973	17,569,933
Gain on disposition of real estate	19,817	14,874	19,828
Operating income	1,259,875	1,087,989	1,078,682
Equity income (loss) from unconsolidated subsidiaries	160,925	324,664	210,207
Other income (loss)	28,907	93,020	9,405
Interest expense, net of interest income	85,754	98,685	126,961
Write-off of financing costs on extinguished debt	2,608	27,982
Income before provision for income taxes	1,361,345	1,379,006	1,171,333
(Benefit of) provision for income taxes	69,895	313,058	467,757
Net income	1,291,450	1,065,948	703,576
Less: Net income attributable to non-controlling interests	9,093	2,729	6,467
Net income attributable to CBRE Group, Inc.	1,282,357	1,063,219	697,109
Eliminations [Member]
Condensed Statement of Income Captions [Line Items]
Income from consolidated subsidiaries	(2,829,815)	(2,739,432)	(1,859,899)
Income before provision for income taxes	(2,829,815)	(2,739,432)	(1,859,899)
Net income	(2,829,815)	(2,739,432)	(1,859,899)
Net income attributable to CBRE Group, Inc.	(2,829,815)	(2,739,432)	(1,859,899)
Parent [Member]
Condensed Statement of Income Captions [Line Items]
Operating, administrative and other	1,000
Total costs and expenses	1,000
Operating income	(1,000)
Income from consolidated subsidiaries	1,283,103
Income before provision for income taxes	1,282,103
(Benefit of) provision for income taxes	(254)
Net income	1,282,357
Net income attributable to CBRE Group, Inc.	1,282,357
Parent [Member] | Reportable Legal Entities [Member]
Condensed Statement of Income Captions [Line Items]
Operating, administrative and other		24,523	5,661
Total costs and expenses		24,523	5,661
Operating income		(24,523)	(5,661)
Income from consolidated subsidiaries		1,081,643	700,608
Income before provision for income taxes		1,057,120	694,947
(Benefit of) provision for income taxes		(6,099)	(2,162)
Net income	1,282,357	1,063,219	697,109
Net income attributable to CBRE Group, Inc.		1,063,219	697,109
CBRE Services [Member]
Condensed Statement of Income Captions [Line Items]
Operating, administrative and other	1,036
Total costs and expenses	1,036
Operating income	(1,036)
Interest expense, net of interest income	(31,037)
Income from consolidated subsidiaries	1,262,674
Income before provision for income taxes	1,290,067
(Benefit of) provision for income taxes	6,964
Net income	1,283,103
Net income attributable to CBRE Group, Inc.	1,283,103
CBRE Services [Member] | Reportable Legal Entities [Member]
Condensed Statement of Income Captions [Line Items]
Operating, administrative and other		1,156	1,972
Total costs and expenses		1,156	1,972
Operating income		(1,156)	(1,972)
Other income (loss)		1	1
Interest expense, net of interest income		(32,031)	(10,648)
Write-off of financing costs on extinguished debt		27,982
Income from consolidated subsidiaries		1,079,469	695,245
Income before provision for income taxes		1,082,363	703,922
(Benefit of) provision for income taxes		720	3,314
Net income	1,283,103	1,081,643	700,608
Net income attributable to CBRE Group, Inc.		1,081,643	700,608
Guarantor Subsidiaries [Member]
Condensed Statement of Income Captions [Line Items]
Revenue	13,550,005
Cost of revenue	10,836,412
Operating, administrative and other	1,705,837
Depreciation and amortization	265,220
Intangible asset impairment	89,787
Total costs and expenses	12,897,256
Gain on disposition of real estate	19,432
Operating income	672,181
Equity income (loss) from unconsolidated subsidiaries	162,019
Other income (loss)	7,842
Interest expense, net of interest income	80,604
Royalty and management service (income) expense	(92,728)
Income from consolidated subsidiaries	284,038
Income before provision for income taxes	1,138,204
(Benefit of) provision for income taxes	(124,470)
Net income	1,262,674
Net income attributable to CBRE Group, Inc.	1,262,674
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement of Income Captions [Line Items]
Revenue		11,998,469	10,702,005
Cost of revenue		9,513,947	8,517,114
Operating, administrative and other		1,715,150	1,437,641
Depreciation and amortization		271,378	239,863
Total costs and expenses		11,500,475	10,194,618
Gain on disposition of real estate		7,705	6,037
Operating income		505,699	513,424
Equity income (loss) from unconsolidated subsidiaries		323,080	206,655
Other income (loss)		103,657	22
Interest expense, net of interest income		329,083	110,494
Royalty and management service (income) expense		(61,626)	66,191
Income from consolidated subsidiaries		578,320	464,046
Income before provision for income taxes		1,243,299	1,007,462
(Benefit of) provision for income taxes		163,830	312,217
Net income	1,262,674	1,079,469	695,245
Net income attributable to CBRE Group, Inc.		1,079,469	695,245
Nonguarantor Subsidiaries [Member]
Condensed Statement of Income Captions [Line Items]
Revenue	10,344,086
Cost of revenue	7,852,601
Operating, administrative and other	1,728,136
Depreciation and amortization	174,004
Total costs and expenses	9,754,741
Gain on disposition of real estate	385
Operating income	589,730
Equity income (loss) from unconsolidated subsidiaries	(1,094)
Other income (loss)	21,065
Interest expense, net of interest income	36,187
Royalty and management service (income) expense	92,728
Income before provision for income taxes	480,786
(Benefit of) provision for income taxes	187,655
Net income	293,131
Less: Net income attributable to non-controlling interests	9,093
Net income attributable to CBRE Group, Inc.	284,038
Nonguarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Statement of Income Captions [Line Items]
Revenue		9,341,619	7,926,782
Cost of revenue		6,935,265	5,787,985
Operating, administrative and other		1,624,944	1,413,446
Depreciation and amortization		180,610	166,251
Total costs and expenses		8,740,819	7,367,682
Gain on disposition of real estate		7,169	13,791
Operating income		607,969	572,891
Equity income (loss) from unconsolidated subsidiaries		1,584	3,552
Other income (loss)		(10,638)	9,382
Interest expense, net of interest income		(198,367)	27,115
Royalty and management service (income) expense		61,626	(66,191)
Income before provision for income taxes		735,656	624,901
(Benefit of) provision for income taxes		154,607	154,388
Net income	$ 293,131	581,049	470,513
Less: Net income attributable to non-controlling interests		2,729	6,467
Net income attributable to CBRE Group, Inc.		$ 578,320	$ 464,046